This invention relates to a method and apparatus for radiation detection. More specifically, this invention relates to a method and apparatus for radiation detection in a high temperature environment.
The detection of radiation through the use of scintillating material has been successfully employed in the past in a variety of contexts. In this, light is produced by a scintillating material in response to incident radiation. This light is operably converted to an electrical signal through the use of a photomultiplier (“PMT”) and this electrical signal can be used to determine the amount and strength of the incident radiation.
In conventional radiation detectors utilizing scintillating material, the scintillating material and PMT are usually two separate components. Each is fabricated independently and they are brought together at a final stage of construction. The common practice in creating this type of detector is to first cut and polish the scintillating material to the required shape and then encapsulate it within a light-tight, mechanically protective container with optically reflective material on all sides except for one of the end faces to allow the scintillator light to be transmitted to the PMT cathode. An optical window is then attached to this open end through the use of a coupling agent such as silicone. The clear face of the scintillating material is then coupled with a PMT using another coupling agent.
One problem with conventional scintillation-type radiation detectors is the fact that at each of the couplings, photons created in the scintillation process are abated because of a mismatch in the indices of refraction or because of absorption.
Prior attempts to remedy the problem of photon loss have primarily been directed to decreasing the size of the gaps between the scintillator, the window, and the PMT. Work has also been envisioned in the selection of the type of window into the PMT in hopes of transmitting the maximum amount of light from the scintillating material. Other prior constructions have deposited the photocathode directly on the scintillating material.
All of these approaches suffered from one or more limitations. While the decrease in the size of the interface gaps is helpful, it is not possible to eliminate gaps entirely. As such, photons continue to be lost in traversing gaps and coupling agents. Window design entails compromises and direct deposit applications have not been useful in high temperature environments.
Scintillation type radiation detectors find useful application in a variety of environments. One application of particular interest in the petroleum industry is the use of scintillation technology to make density and other measurements within a well hole. Downhole applications, however, present a challenge because of the temperature at which the radiation detector must operate and the fact that increased vibration may affect the integrity of the interfaces between components
The difficulties and limitations suggested in the preceding are not intended to be exhaustive, but rather are among many which demonstrate that although significant attention has been devoted to increasing efficiency and sensitivity in scintillating type radiation detectors, the prior attempts do not satisfy both the desired increase in efficiency and the need for operation in noisy, high temperature environments.